A. Field of the Invention
The present invention relates generally to carbonless paper products. More specifically, the present invention relates to the pad coating for carbonless paper products.
B. The Prior Art
Carbonless paper products are known in the art. These products function to afford one the ability to make "carbons" or duplicates of a document, bill of lading, invoice, or the like, without the need for carbon paper. As is clearly evident, carbon paper has several disadvantages. These disadvantages include the fact that it is a cumbersome, sometimes difficult, process to insert carbon paper between the sheets of paper upon which a duplicate is to be made and the process of so inserting the carbon paper and removing same can be messy. To resolve some of the disadvantages inherent with carbon paper, carbonless paper was developed.
Briefly, carbonless paper typically includes a paper substrate upon which a front coating (hereinafter "CF") and a back coating (hereinafter "CB") are coated on respective sides of a paper substrate. The CF and CB have compositions such that upon a mixing of the CF and CB a mark is generated.
Accordingly, in constructing a carbonless paper product, the sheets of paper are oriented so that the sheets of paper on which a duplicate copy is to be made all include, on a front surface thereof, a CF layer. This CF layer is located in juxtaposition to a CB layer that is located on the back surface of all of the sheets of paper from which a duplicate is to be generated. An inter mixing of the CF and CB layer is created by the exertion of a sufficient force on a front face of the paper. This results in the generation of a mark, on the underlying layers of the carbonless paper, that corresponds to the mark made on the original front surface of the top sheet.
Carbonless paper has especially enjoyed commercial success in applications where two or three duplicates of a form are required. Such forms include, for example, bills of lading, invoices, credit card receipts, and the like. These documents typically comprise two or more sheets that are secured together by some means. One of the most common ways to secure the sheets together is to use an adhesive coating that is coated along one edge of the sheets. This typically is called a fan-out padability adhesive. Such adhesives are commercially available from the Appleton Paper Co., Minnesota Mining and Manufacturing Co., and Mead Paper Co., among others.
One of the disadvantages in using such an adhesive coating, however, is that these form sets are typically generated by the thousands and it is not economical to separately coat each set of sheets that define the form. Instead, a pad coat is utilized on at least the bottom of the last sheet of each set of the forms, and often on the top of the first sheet of the form set as well. The function of the pad coats is to prevent the individual sets of forms from sticking together when the fan-out padability adhesive is applied thereto. The use of a pad coat results in the individual sheets that define one form set being secured together but not the form sets themselves. The capacity of the last sheet of one form set to separate from the first sheet of a next form set is called "fanapart" or "padability."
Although pad coats have been developed that provide some fanapart of the form sets after an adhesive is applied, these coats have not been entirely satisfactory. One problem is that, in many instances, the back of the last sheet of a form set must contain instructions, contract terms, or other necessary information. Accordingly, any such pad coating coated on the back surface of the last sheet must allow this surface to be printed thereon. However, some prior pad coats, when coated on a paper product, create a surface that has poor printability.
Still further, it is necessary for any such pad coat to have characteristics such that it can coat the base paper, or paper substrate, through commercial production techniques.